US President Barack Obama travelled to the northeastern state of Pennsylvania yesterday, a key political battleground important to Democrats as they hope to retain control of the U.S. Congress in November midterm elections. The President's latest campaign trip came after he took part in a more than hour-long live television discussion about the nation's economy. The resident was the keynote speaker at two Philadelphia fund raising events for Representative Joe Sestak, a former U.S. Navy admiral turned politician who is in a tough battle against Republican Pat Toomey for Pennsylvania's open U.S. Senate seat. It was the Mr. Obama's first campaign appearance for Sestak, who against White House wishes ran against and defeated Arlen Specter, the former long-time Republican senator who switched parties to join Democrats, in a primary contest earlier this year. The two candidates are challenging each other's credentials in television ads. President Obama and Vice President Joe Biden are scheduled to campaign heavily for Democrats until November with stops in crucial states such as Ohio, Wisconsin, Nevada and again in Pennsylvania, where outcomes could determine control of the U.S. Senate and House of Representatives as well as key governorships.